#include<bits/stdc++.h>
using namespace std;
int main(){
	int n;
	cin>>n;
	float   f;
	f=(n-2)*180.0/n;
	printf("%.1f",f); 
}
/**************************************************************
	Problem: 1317
	User: wangyousi
	Language: C++
	Result: Accepted
	Time:14 ms
	Memory:2072 kb
****************************************************************/